Light emitting dies (LED or LEDs) are solid state devices that convert electric energy to light, and generally comprise one or more active layers of semiconductor material sandwiched between oppositely doped layers. When a bias is applied across the doped layers, holes and electrons are injected into the active layer where they recombine to generate light. As the bias or voltage is applied to the semiconductor, the energy that is used by the LED is converted into light energy, and the light is emitted from the active layer and from all surfaces of the LED. In order to use an LED chip in a circuit or other like arrangement, it is known to enclose an LED chip in a package to provide environmental and/or mechanical protection, color selection, focusing and the like. An LED package can also include electrical leads, contacts or traces for electrically connecting the LED package to an external circuit. In a typical LED package, an LED chip can be mounted on a reflective cup by means of a solder bond or conductive epoxy. One or more wire bonds can connect the ohmic contacts of the LED chip to leads, which may be attached to or integral with the reflective cup. The reflective cup may be filled with an encapsulant material containing a wavelength conversion material such as a phosphor. Light emitted by the LED at a first wavelength may be absorbed by the phosphor, which may responsively emit light at a second wavelength. The entire assembly can then be encapsulated in a clear protective resin, which may be molded in the shape of a lens to collimate the light emitted from the LED chip. While the reflective cup may direct light in an upward direction, optical losses may occur when the light is reflected (i.e. some light may be absorbed by the reflector cup instead of being reflected). In addition, heat retention may be an issue for such a package, since it may be difficult to extract heat through the leads.
A conventional LED package may be more suited for high power operations in one or more LED chips are mounted onto a carrier such as a printed circuit board (PCB) carrier, substrate or submount. Such a package can also generate more heat. A metal reflector mounted on the submount can surround the LED chip(s) and can reflect light emitted by the LED chips away from the package. The reflector can also provide mechanical protection to the LED chips. One or more wirebond connections can be made between ohmic contacts on the LED chips and electrical traces on the carrier. The mounted LED chips can then be covered with an encapsulant, which may provide environmental and mechanical protection to the chips while also acting as a lens. The metal reflector is typically attached to the carrier by means of a solder or epoxy bond.
While such a package may have certain advantages for high power operation, there may be a number of potential problems associated with using a separate metal piece as a metal reflector. For example, small metal parts may be difficult to manufacture repeatable with a high degree of precision at a reasonable expense. In addition, since the reflector is typically affixed to a carrier using an adhesive, several manufacturing steps may be required to carefully align and mount the reflector, which may add to the expense and complexity of the manufacturing process for such packages.
For higher powered operation, it may also be difficult to dissipate heat generated by the LED chip. This can be true for packages employing LEDs of specific light ranges, for example, LEDs that emit red and/or red-orange light. Submounts can be made of materials such as ceramics that are robust but do not efficiently conduct or dissipate heat which can result in reduced efficiency and output of the LED package as well as reduced lifetime or failure of the package. Other factors involved in using conventional packages can also reduce and/or limit the lumen performance, efficiency and/or lifetime of such LED packages.